Renewable fuse structure



Mind! 26, 1940- J., B. GRIFFITH 2,195,147

RENEWABLE FUSE STRUCTURE,

Filed July 29, 1931 iZc'giZ Patented Mar. 26, 1940 UNITED STATES PATENT j OFFICE.

1 Claim.-

This invention relates to a renewable fuse structure. and is more particularly concernedwith simplification and reduction of the number of parts therein. One of the features of the present invention is the provision of a renewable fuse structure comprising an external tube of insulating material and in internal rigidly-assembled support for a fusible link, these parts being capable of quick assembly and disassembly by a simplethreaded joint or the like.

Another feature of the present invention is the provision of an external insulating body having a shoulder therein, together with an assembled holding structure for the fusible link, the holding structure comprising sealing means engaged with said shoulder when assembled and also including interengaging screw threads on said external member and on said holding structure for assuring the desired relationship.

With these and other features as objects in view as will appear in the course of the following speciflcation and claim an illustrative formof construction according to the-present invention is 5 shown in the accompanying drawing in which:.

Figure 1 is a sideelevation ofa renewable fuse structure according to this invention.

Figure 2 is an axial diametrical section through the same substatntially on line 22 of Figure 1. 30 Figure 3 is an exploded view showing parts of one end of the holding structure. 4

Figure 4 is an enlarged sectional view 'of th other end indicating a gas escape channel.

Figure 5 is a perspective view of a fusible link 35 for employment in the device.

Figures 6 and 7 are views showing modifications in the construction of the structure.

In the drawing, the renewable fuse structure is illustrated as comprising an external insulating body which is shown as a sleeve III of vulcanized fiber in the formshown by Figures 1 to 4.-- For reasonsof cheapness, it has been found advantageous to make this tube from a piece of tubing having an external diameter desired for the fin-' 45 ished fuse structure and having an internal diameter slightly greater than the width of the contact terminal blades. available. The tubing is cut to the desired standard length, and is then bored to increase the in- 50 ternal diameter from one end up to an inwardly extended flange Illa which provides a shoulder as will be described hereinafter. This boring operation can be quickly and simply effected, and

is followed by a similar threading operation to 55 provide threads Illb at the open larger end of the Such tubing is commercially tube. It is preferred to form this sleeve of insulating and infusible material such as the vulcanized fiber referred to. When formed, it is also preferred to coat and seal the surface of this material by the employment of a liquid coating 5 composition which is non-inflammable under the conditions of service, and is not changed by the action of heat or gases released at the time of disruption: such a composition is referred to in my co-pending application, Serial Number 10 156,395, filed of even date herewith and entitled renewable fuse structure.

I so that a narrow extension or to'gnue Ila, I 20. is 20 provided at the interior end, and having a hole :I I0, I20. It will be noted that these two blades II, I2 may be identical in size and shape.

The blade I I has its narrow portion Ila passed through and tightly fitting in the correspondingly-shaped slot I3a of a closure disc l3. This disc has an external diameter which is greater than the original internal diameter of the outer tube II] when formed as above described, and less than the internal diameter of the bore hole formed therein.

, The tongue Ila of a contact blade II extends inside of the disc l3 and overlaps a spacer member I4 which appropriately may be of fiber material. The length of this spacer I4 is dimensioned to the desired distance between-the disc I3 and a corresponding head 20 at the other end of the structure.- Apertures are provided therein at such'distances that, when these apertures are aligned with the holes I I0, I20, the ends of spacer member Il'abut against the disc l3 and the head 20: These holes are appropriately spacedaccording to the dimensions of the fusible link FL (Figure 5) -to be employed. At the other end, the head 20 has a threaded exterior for engagement with the screw threads. l llband has a s10t20a. closely receiving the tongue I2a of the blade I2.

It is unnecessary to have the head 20 solid, and

it may be hollowed out, preferably from the exterior as shown in Figure 4."

"The rules of the board of fire underwriters require that such fuse structures should be so devised that there is no puil'. or blast of hot gas at the time of disruption. With the present arrangement, the threaded engagement of the threads 201) on the head 20 with the threads llib causes a seal to be eflected between the disc l3 and the shoulder Ilia. Further, it is preferred to cut the threads 10b and the threads 20b both with sharp bottom or V-threads. However, the bore in the body I0 is made larger in diameter than the base or root diameter of the threads 20b so that a small spiral passage remains when the parts are threaded together, to permit slow adjustment of pressure conditions such as those occurring naturally in operation or created by the thermal heating or air, etc., within the fuse structure upon disruption. It will be noted that the parts may be cheaply and easily constructed so that the normal tolerances will provide joints which have crevices of such reduced dimensions that the rules are satisfied.

In using the structure, the support for the iusible link is assembled by passing the bolts 18 through washers l'l, through the apertures in the spacer I4, and through the reduced portions Ila, l2a. A further washer i8 and a nut I9 is then placed upon each bolt. It is now possible to slip the fusible link FL (Figure 5) beneaththe washer i8, this link being held away from the spacer member by the thickness of the reduced portion or tongue ila, I211 (Figure 2). -The nuts I! are then tightened and the support with the link secured thereto may then be introduced into the tubular housing ill. The threads are brought together and are tightened by the usual relative rotations until the disc i3 is pressed tightly against the shoulder la.

The device is used in the normal manner. When the fusible link has been disrupted, the entire device can be removed from the fuse block and the parts unscrewed and separated. The nuts I! are released and fragments of the fusible link FL ejected. A new fuse link is slipped beneath the washers I8, the nuts are tightened again, and the assembly is screwed back into the tubular housing ll.

While a cheap and advantageous construction has been described above in respect to forming the tubular housing in integrally by boring and tapping a piece of fiber, it is obvious that this construction may be provided in other ways. From Figure 6, for example, it will be noted that a tubing Illa: having a larger interior diameter may be employed, together with a short ring I01! for providing a shoulder to receive the disc l3.

- The ring I011 may be held in position by cementing as shown at the joint lllw. Also small rivets or pins 30 may be introduced if desired.

In Figure 7 the ring I011 is illustrated as being of conductive material, and the pins 30 pass to the exterior and may be utilized for contact with a neon light terminal to determine whether or not the fusible link has been disrupted.

It is obvious that the invention is not limited solely to the forms of construction shown but that it may be varied in many ways through the scope of the appending claim.

I now claim and desire tosecure by United States Letters Patent the following:

A renewable fuse structure comprising an outer tubular housing of insulating material, means providing a continuous shoulder in the bore of said tubular housing spaced inwardly from one end, and internal threads in the wall of said bore adjacent the other end; and a supporting assembly for a fusible link and including contact blades having narrow tongues extending into the tubular housing, an end disc with a slot receiving and closely fitting one of said tongues, a threaded head in the bore of the tubular housing with a slot receiving and closely fitting the other of said tongues, an insulating spacer member, said tongues and spacer member having aligned apertures, and bolts passing through the apertures and effective for holding the disc and the head respectively clamped between the spacer member and the shoulders on said contact blades and for holding a fusible link in conductive relation to said contact blades, one of said threads being of less depth than the groove engaged thereby so that a portion of the latter remains open and establishes communication between the interior of the tubular housing and the atmosphere; said assembly with the disc foremost being insertabie through the threaded end of the tubular housing and the assembly being rotatable through turning of a contact blade to engage the threads of said head with said internal threads for holding said disc in sealing contact against said flange.

JOHN B. GRIFFITH. 

